This invention pertains to repairing the blades (vanes) of a gas turbine and, more particularly, to a cutter assembly and process for removing and restoring the blades or vanes of a gas turbine.
Gas turbines are extensively used in oil refineries, such as with catalytic cracking units, ultracracking units, power houses, and cogeneration plants, as well as in chemical plants, power plants, and other industrial sites to generate power.
In gas turbines, the moving rotor blades and the stationary stator blades experience considerable wear over time due to erosion from dust, metal chips, and other solid particulates and chemical corrosion from corrosive gases, such as sulfur oxides and nitrogen oxides, in the surrounding environment. Gas turbines with worn blades are inefficient and often ineffective and must be periodically repaired.
The repair and restoration of gas turbine blades (vanes) is not an easy job. It usually requires a team of at least four or five people working 7 to 10, 24-hour, days to fix and restore the gas turbine blades. During such repair, the associated refinery equipment and operating unit are often required to be shut down, thereby causing loss of revenue ranging from about 1.75 to 10 million dollars. Not only is such repair expensive from a standpoint of loss of revenue, but it is tedious, cumbersome, time-consuming, and difficult.
Over the years a variety of methods have been suggested for overhauling, repairing, and replacing worn stator blades of a gas turbine. Such prior art methods include heating, hammering, acetylene torching, chemical dissolution, plasma deposition, machining, and punching. In one common prior art method, the stator blades are heated to a temperature of 600.degree. F. to 800.degree. F. and the blades, base ring sections (shrouds), and/or the compressor case of the gas turbine are hammered. Heating to such high temperatures followed by hammering can cause considerable damage to the compressor case, thereby requiring replacement, further downtime, and considerable expense.
Typifying, some of the different prior art methods, techniques, and equipment for repairing turbine blades, as well as other machines and machining operations, are those shown in U.S. Pat. Nos. 1,795,262; 1,798,224; 3,099,902; 3,421,265; 3,641,709; 4,141,124; 4,291,448; 4,291,973; 4,376,356; and 4,464,865. The above prior art methods, techniques, and equipment have met with varying degrees of success.
It is, therefore, desirable to provide an improved cutter assembly and process for revamping gas turbine blades.